To produce a monolithic capacitor, which is one example of a monolithic electronic part, the following methods have been being employed.
One method comprises forming an electroconductive inner electrode film on a ceramic green sheet, preparing a plurality of such ceramic green sheets each having the electroconductive film formed thereon, laminating these ceramic green sheets to obtain a ceramic laminate, then sintering the ceramic laminate, and thereafter attaching, to said sintered ceramic laminate, electroconductive films to provide outer electrodes, thereby to finally obtain a monolithic capacitor. To form the electroconductive inner electrode film on the ceramic green sheet in this method, screen-printing is generally employed. (This method is hereinafter referred to as "prior art method 1".)
In general, monolithic capacitors of this type are required to be small-sized while having a large capacitance. In order to produce such small-sized monolithic capacitors having a large capacitance, generally, the ceramic green sheets and also the inner electrode electroconductive films are made thin.
However, there is a limit to how thin and uniform the electroconductive films can be made on ceramic green sheets by screen-printing. When a plurality of such ceramic green sheets, each having an electroconductive film screen-printed thereon, are laminated to give a ceramic laminate, the difference in thickness between the area of the ceramic green sheet having the electroconductive film formed thereon and the area thereof not having the film brings about a difference in level therebetween. The difference in level often has an influence on the electrical characteristics of the monolithic capacitor comprising the ceramic laminate. This problem is more serious when the thickness of the ceramic green sheets is smaller.
In order to solve this problem, studies are being made of employing electroless plating, in place of screen-printing, for forming electroconductive films to be inner electrodes on ceramic green sheets.
One electroless plating method for forming an electroconductive film to provide an inner electrode on a ceramic green sheet is as follows:
An electroconductive film is formed on the whole surface of a carrier film, such as a polyester film, through electroless plating, and then this is etched to give a pattern having a desired profile. Next, a ceramic green sheet is formed over the carrier film having thereon such a patterned electroconductive film, and thereafter the carrier film is peeled off from the ceramic green sheet, whereby the electroconductive film is transferred onto the ceramic green sheet. In that manner, a ceramic green sheet is obtained having an electroconductive inner electrode film formed thereon. (This method is hereinafter referred to as "prior art method 2".)
Another electroless plating method is as follows:
As disclosed in Japanese Patent Application Laid-Open No. 63-169015, the disclosures of which are incorporated by reference, a liquid comprising an activating catalyst is applied onto a ceramic green sheet selectively at predetermined areas thereof by stamping or printing equipment, and then the ceramic green sheet is dipped in an electroless plating bath to thereby form an electroconductive inner electrode film on the selected areas of the ceramic green sheet coated with the activating catalyst liquid. (This method is hereinafter referred to as "prior art method 3".)
According to the above-mentioned electroless plating methods of forming electroconductive films, more uniform and thinner electroconductive films can be formed on ceramic green sheets than those formed according to the prior art screen-printing method 1. Therefore, when a plurality of the ceramic green sheets each having such a more uniform and thinner electroconductive film formed thereon are laminated to give a ceramic laminate, the resulting ceramic laminate is prevented from having a difference in level between the non-coated area and the coated area in each sheet.
However, the conventional electroless plating methods for forming electroconductive films have some problems such as those mentioned below.
First, in the prior art method 2, since the electroconductive film formed on the whole surface of the carrier film is etched to give a pattern having a desired profile, large amounts of organic solvents and acids must be used. Such organic solvents and acids bring about an increase in the cost of production. In addition, large amounts of organic acids and acids used often dissolve or swell the carrier film.
On the other hand, in the prior art method 3, the liquid of an activating catalyst is applied onto the ceramic green sheet selectively at predetermined areas by stamping or printing equipment. The use of stamping and printing equipment imposes limits on the available resolution and accuracy in the positions to be selected. Therefore, fine, precision patterns are difficult to obtain.